I have tried your suggestions of using the Jam wrench to try and free the bottom but it will not budge at all. In fact the wrench is being bent trying to rotate it one way and the other.
Is the insinkerator broken or is it worth trying to have it repaired by a qualified service agent?

Sturgess, February 2011

Sounds like it may be completely seized up. Probably cheaper to go buy a new one than have the old one completely dismantled & repaired.

George, March 2011